This invention relates to cold pack devices. More specifically, this invention relates to cold pack devices which can be utilized for treating injury and reducing pain.
The treatment of injury by the application of cold pack devices is known as cryotherapy or cold treatment. For many years, physicians, trainers and coaches of athletic teams have utilized the application of cold to treat sprains or fractures. It is also well known that cold is an effective medical treatment for other medical problems as well. Cold is also used to slow bleeding, for example, nosebleeds and the like, to reduce the pain and swelling of wounds, to slow the absorption of snake bite poisons by reducing the blood flow in the bite area and for other medical applications.
When an injury occurs, the blood vessels in the area dilate and release fluid into the injured tissue, thus causing swelling and pain. This swelling is due to damage of the capillary wall which results in seepage of fluid to the injury site. Reducing the circulation in the area by application of cold reduces the accumulation of fluid and thereby minimizes the swelling in the area. In the management of injuries the prevention of swelling is desirable. The early application of a cold pack device to the injured area constricts the blood vessels and reduces the loss of fluid into the injured area. Thus, while cold therapy reduces the circulation to the site of injury, it is only for a relatively short period of time. It prevents the swelling which would prolong the period of disability and thus retard healing.
Cold also relieves the pain of an injury by desensitizing nerve endings. When cold is first applied to an affected area, there is a gradual onset of numbness produced by a slowing of the sensory conduction. Then there is an inhibition of all sensory perception of the area, including pain. The application of cold to an injured surface also helps to stop bleeding. For example, cold is effective in reducing the disabling effects of bruises and sprains. It slows the leakage of blood by reducing the blood flow to the area and therefore from ruptured capillaries. The black-and-blue discoloration of the skin is due to a leakage of blood from ruptured blood vessels. By applying a source of cold to the injured area, the temperature of the skin drops and the blood vessels constrict. This helps to promote the clotting of the ruptured capillaries, thereby reducing local blood loss and swelling.
In the early treatment of first or second degree burns, the application of cold will again slow the blood flow and thereby reduce the massive swelling which usually accompanies burns.
Thus, it is well known that the prompt and efficient medical application of cold has desirable medical advantages. The old and long-accepted medical method of supplying needed cold was to fill a rubber bag with ice, wrap the icebag with a towel, and apply it to the area of injury. This method, although effective, often takes considerable time and is obviously impossible at the scene of an accident, on an athletic field, or in a first-aid station or hospital emergency department.
To eliminate inconvenience and to facilitate the use of cold, various disposable cold pack devices that require no refrigeration have been developed and made commercially available. These devices generally consist of chemicals in a plastic bag containing two or more compartments in order to keep the chemicals separated until actuation is desired. The "instant ice pack," as these devices are sometimes referred to, are initiated by rupturing or removing the separating means to produce an endothermic reaction, that is, as a result of the chemical reaction, cold is produced by the absorption of heat from the surroundings. These devices in many cases have various negatives which reduce their effectiveness and, therefore, their desirability. For example, some of these cold pack devices contain materials which do not have negative heats of reaction sufficient to result in a final temperature within the optimum therapeutic range, i.e., 30.degree.-45.degree.F. Temperatures below 30.degree.F. may be desirable for certain applications. Other cold pack devices have undesirable slow activation times while still others present cost problems or problems at shipping or storage temperatures. One of the most significant shortcomings of the prior products has been the inability of such cold pack devices to produce or maintain the desired effective temperature over a sustained period of time. Still another significant shortcoming of the presently available cold packs is that such products when activated at higher ambient temperatures, i.e., 90.degree. to 100.degree.F., do not drop to the desired therapeutic temperature range.
Typical attempts of the prior art to form a desirable cold pack device include U.S. Pat. Nos. 2,898,744 and 3,058,313. U.S. Pat. No. 2,898,744 discloses chemical freezing packages which consist of chemicals such as sodium acetate, ammonium chloride, sodium nitrate, sodium thiosulfate, potassium iodide, calcium chloride, and ammonium nitrate which upon the addition of water result in a marked reduction of temperature.
U.S. Pat. No. 3,058,313 discloses a cooling pack comprising a crystalline form of a chemical reagent in admixture or contact with a dry form of a chemical. The dry form of chemical is said to be ammonium nitrate (NH.sub.4 NO.sub.3) and the crystalline reagent is said to be sodium carbonate decahydrate (Na.sub.2 CO.sub.3 . 10H.sub.2 O) or a similar chemical reagent. It is further indicated that the water of crystallization is sufficient to cause the necessary freezing reaction although additional water may be added if desired.
Cold pack devices prepared in accordance with the above and other similar teachings do not result in completely satisfactory products as previously discussed. For example, such products do not have the desired fast activation and long duration of cold and, furthermore, many of these formulations do not have a reusability feature.
For the purposes of this invention, the term "fast activation" is defined as the rapid drop in temperature of the cold pack device after it has been activated. The optimum standards set for fast activation for the purposes of this invention are that three minutes after activation the cold pack should fall to or below about 10.degree.F. when activated at 40.degree.F; to about 45.degree.F. or below when activated at 70.degree.F. or higher.
The term "duration of cold" as used in describing the present invention shall mean the length of time the activated cold pack remains at or below 45.degree.F. The term "reusability" as used hereinafter shall mean that a cold pack device does not freeze solid but remains conformable and available for immediate use when placed in a freezer or other similar temperature regulating apparatus at 0.degree.F. for 24 hours after the cold pack device has been activated and the endothermic reaction has ceased.